The electron microscope is an important tool used, for example, in material analysis. A conventional transmission electron microscope (TEM) generates a magnified image of a sample on a space resolving image sensor. Conventional electron microscopes are also used to analyze a distribution of scattering angles experienced by electrons traversing a sample, wherein a diffraction image of the sample is analyzed in such systems.
Conventional electron microscopes are so-called in-lens systems including an electromagnet generating a magnetic field having an effect on the electron beam of two electron-optical lenses arranged in the beam path. An object mount is provided for mounting a sample to be analyzed in an object plane, wherein the object plane is arranged between the two electron-optical lenses. The electron-optical lens arranged in the beam path upstream of the object plane has a function of a condenser lens focusing the electron beam in the object plane. The electron-optical lens arranged in the beam path downstream of the object plane has a function of an objective lens generating a magnified image of the object plane. A projection system is arranged in the beam path downstream of the two electron-optical lenses, wherein the projection system has plural electron-optical lenses and generates a magnified image of a diffraction plane of the objective lens on a detector.
The detector may include a detector component centrally arranged on an optical axis of the objective lens and of the projection system in order to detect bright field electrons. Bright field electrons are electrons having traversed the sample substantially without scattering. The detector may further include plural detector components arranged at a distance from the optical axis in order to detect dark field electrons. Dark field electrons are electrons which have been significantly scattered upon traversing the sample.
A scanning electron microscope (SEM) includes a deflector arranged in the beam path upstream of the object plane in order to scan the focused electron beam across the sample such that image information relating to the object can be obtained by scanning the focused electron beam across the object and detecting intensities of bright field electrons and/or dark field electrons for a plurality of locations in the object plane.
The projection system used for imaging of the diffraction plane of the objective lens onto the detector has disadvantages in that it is complicated, since the diffraction plane to be imaged is arranged at a large distance from the lenses of the projection system, it is expensive and requires significant space such that a length of the beam path between an electron source and the detector is high.